1. Field of the Invention
The invention relates in general to a system and a method for accurately metering, accumulating, and accounting for the by-product waste stream generated from a solid deposition modeling process. In addition, the system allows operator intervention during the fabrication process and can be integrated with a sealed waste removal system wherein reactive materials can be employed without special handling procedures.
2. Description of the Prior Art
Recently, several new technologies have been developed for the rapid creation of models, prototypes, and parts for limited run manufacturing. These new technologies can generally be described as solid freeform fabrication, herein referred to as “SFF”. Some SFF techniques include stereolithography, selective deposition modeling, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, fused deposition modeling, particle deposition, laser sintering, and the like. In SFF, complex parts are produced from a modeling material in an additive fashion as opposed to conventional fabrication techniques, which are generally subtractive in nature. For example, in conventional fabrication techniques material is removed by machining operations or shaped in a die or mold to near net shape and then trimmed. In contrast, additive fabrication techniques incrementally add portions of a build material to targeted locations, typically layer by layer, in order to build a complex part.
SFF technologies typically utilize a computer graphic representation of a part and a supply of a build material to fabricate the part in successive layers. SFF technologies have many advantages over the prior conventional manufacturing methods. For instance, SFF technologies dramatically shorten the time to develop prototype parts and can quickly produce limited numbers of parts in rapid manufacturing processes. They also eliminate the need for complex tooling and machining associated with the prior conventional manufacturing methods, particularly when creating molds for casting operations. In addition, SFF technologies are advantageous because customized objects can be produced quickly by processing computer graphic data.
There are a wide variety of build materials that are used in various SFF techniques. These materials are typically applied in the form of a powder, liquid, gas, paste, foam, or gel. Recently, there has developed an interest in utilizing highly viscous paste materials in SFF processes to achieve greater mechanical properties. In addition, an interest has recently developed in reproducing visual features such as color on the three-dimensional objects produced by SFF processes. This has produced a need to develop special additives for the build materials along with new dispensing systems to enable the production of these visual features when building the three-dimensional objects.
One category of SFF that has emerged is selective deposition modeling, herein referred to as “SDM”. In SDM, a build material is physically deposited in a layerwise fashion while in a flowable state and is allowed to solidify to form an object. In one type of SDM technology the modeling material is extruded as a continuous filament through a resistively heated nozzle. In yet another type of SDM technology the modeling material is jetted or dropped in discrete droplets in order to build up a part. In one particular SDM apparatus, a thermoplastic material having a low-melting point is used as the solid modeling material, which is delivered through a jetting system such as those used in ink jet printers. One type of SDM process utilizing ink jet print heads is described, for example, in U.S. Pat. No. 5,555,176 to Menhenneft, et al.
Because ink jet print heads are designed for use in two-dimensional printing, special modifications must be made in order to use them in building three-dimensional objects by SFF techniques. This is generally because there are substantial differences between the two processes, thus requiring different solutions to different problems. For example, in two-dimensional printing a relatively small amount of an ink is jetted and allowed to dry or solidify with a significant interest being given to print resolution. Because only a small amount of material is jetted in two-dimensional printing, the material reservoir for the liquid material can reside directly in the ink jet print head while providing the ability to print numerous pages before needing to be refilled or replaced. In contrast, in SDM utilizing an ink jet printhead, a large amount of normally solid material, such as a thermoplastic or wax material, must be heated to a flowable state, jetted, and then allowed to solidify. Furthermore, in SDM dispensing resolution is not as critical as it is in two-dimensional printing. This is generally because, for each targeted pixel location, the amount of material to be jetted in SDM techniques is substantially greater than the amount to be jetted in two-dimensional printing techniques. For example, it may be required to deposit six droplets on a particular pixel location in SDM compared to just one or two droplets in two-dimensional printing. Although the targeting accuracy may be the same, the actual resolution achieved in SDM techniques is generally somewhat less than in two-dimensional printing because the six droplets dispensed may droop or slide towards adjacent pixel locations.
The differences mentioned above are significant and create a number of problems to be resolved. For instance, the amount of material deposited in ink jet based SDM techniques, both in volume and in mass, can be so substantial that it is generally considered impractical to mount a reservoir directly on the ink jet print head to hold all of the material. Thus, it is typical in most SDM systems to provide a large reservoir at a location remote from the print head that is in communication with the ink print head via a material delivery system having a flexible umbilical tube. However, the large container and umbilical tube must be heated to cause at least some of the build material to become or remain flowable so that the material can flow to the dispensing device. Start up times are longer for SDM techniques using ink jet print heads than in two-dimensional printing with ink jet print heads due to the length of time necessary to initially heat the solidified material in the large remote reservoir to its flowable state. In addition, a significant amount of energy is required to maintain the large quantity of material in the flowable state in the reservoir and in the delivery system during the build process. This generates a significant amount of heat in the build environment.
Another problem that is unique to SDM techniques is that the layers being formed must be shaped or smoothed during the build process to establish a uniform layer thickness. Normalizing the layers is commonly accomplished with a planarizer that removes a portion of the material dispensed in the layers. One such planarizer is disclosed in U.S. Pat. No. 6,270,335 to Leyden et al. However, the planarizer produces waste material during the build process that must be handled. This is less of a concern when working with non-reactive materials; however, it is a greater concern when reactive materials are used. For example, most photopolymers are reactive, and excessive contact to human skin may result in sensitivity reactions. Thus, most SFF processes that utilize photopolymer materials require some additional handling procedures in order to minimize or eliminate excessive physical contact with the materials. For example, in stereolithography, operators typically wear gloves when handling the liquid resin and when removing finished parts from the build platform. However, SDM operators who normally handle even non-reactive materials consider additional handling procedures inconvenient and, if possible, would prefer they be eliminated. For reactive materials in SDM systems the issue is compounded and rises above mere inconvenience. Thus, there is a need to provide a material feed and waste system for SDM that can handle reactive materials without requiring the implementation of special handling procedures.
A by-product waste handling system for dealing with the aforementioned waste stream from an SDM process is described in U.S. patent application Ser. No. 09/970,956, entitled “Quantized Feed System For Solid FreeForm Fabrication” and assigned to the assignee of the present invention. In that system the by-product waste material collects in an in-line reservoir and flows from it by gravity for delivery through actuated solenoid valves into waste receptacles. Although workable, that system is improved significantly by the instant invention. A lack of sufficient buffering capacity can result in too much by-product waste material backing up in the system. The amount of by-product waste is not known so the amount of energy (optical or thermal) needed to cure or solidify the material collected is not known. A system is needed that reliably captures all of the waste material, accurately measures it, and delivers measured amounts to a waste collection container without the use of large and expensive vacuum systems. In addition, a system is needed that allows operator intervention to remove and replace waste containers without interrupting a build.
These and other difficulties of the prior art are overcome according to the present invention by providing a new and simpler by-product waste removal system for a solid deposition modeling system utilizing on an automated collection reservoir.